QUALITY ASSURANCE PROCEDURE FOR MONITORING TACROLIMUS (FK506) CONCENTRATIONS IN WHOLE-BLOOD BY IMX ASSAY

A Quality Assurance Program for the IMx assay for FK506 in whole blood samples was established to monitor the performance of the assay in cl inical sites enrolled by Fujisawa USA, Inc. Forty investigative sites participating in the program were required to perform assays to establ ish intraassay variability, interassay variability, and performance on blinded samples. Only two of the sites were required to repeat part o f the program. The intraassay and interassay results at the sites were in good agreement with the target values obtained at Fujisawa Researc h Laboratory. Most of the coefficients of variation (CV) were within /-15%, well within the acceptance range of +/-30%. Only a few values w ere outside the acceptance window. For the blinded samples, the CVs we re variable and depended on the concentration of FK506 in the sample. At lower blood FK506 concentrations (5-10 ng/ml), the mean CVs were of ten outside the acceptance window, and many individual values were not acceptable. At concentrations of 15-50 ng/ml, the CVs were generally acceptable. Thus individual sites can quickly learn to perform the FK5 06 IMx assay and achieve good within- and between-day results. The ass ay of lower blood concentrations of FK506 may show higher variability. Patients are usually monitored for clinical signs of rejection and to xicity in addition to blood FK506 concentrations.